The present invention relates to an auxiliary device of a sewing machine, capable of making three straight stitches and a net-like stitch and particularly to one which can help the net-like stitch securely formed on the cloth at the beginning of the sewing.
Referring to FIGS. 7 and 8 and 9, a conventional sewing machine capable of making three straight stitches and a net-like stitch on a cloth has a needle holder 5, three needles 51 secured to the needle holder 5, and a pressing member 57 provided to press the cloth. The sewing machine further has a lower shuttle needle (not shown) for a net thread to make a net-like stitch and three straight stitches (as shown in FIG. 10) together with the three upper needles 51 on the bottom of the cloth.
To make the above sewing machine capable of working more efficiently, a lower thread cutting device 55 (FIG. 11) is fitted under the flat-bed such that the threads 511 can be cut off automatically at the end of the sewing.
Moreover, referring to FIG. 9, a thread hooking device 54 is fitted to screw holes 512 of the sewing machine; the thread hooking device (FIGS. 13 and 14) was invented by the inventor of the present invention, and patented by R.O.C Intellectual Property Office with patent no. 286691 on Sep. 21, 1996. The hooking device 54 has a hooking plate 541, and an elastic plate 542 which can clip the ends 510 of the threads cut off by the lower thread cutting device 55 for permitting the ends 510 of the threads to be covered by stitches of the next sewing.
However, the above sewing machine can't make net-like stitches on both the upper side and the lower side of a cloth as shown in FIG. 15. To make two side net-like stitches, a shuttle 52 has to be fitted to the sewing machine, and the thread hooking device 54 removed, and a thread guide support 53 (FIGS. 16 and 17) is fitted to the screw holes 512 instead. The upper net thread 531 is passed through a curved hole 532 of the thread guide support 53. Thus, the upper net thread 53 can be made into upper net-like stitches by means of the shuttle 52. The sewing machine capable of making two-side net-like stitches is found to have a disadvantage that three of more lower side net-like stitches would fail to form at the beginning of sewing as shown in FIGS. 17 and 18 because, referring to FIG. 14, when the threads 511 are cut off, the distance L between the right one of the needles 51 and the end 543 of the hooking plate 541 is relatively long as compared with the length (4.about.5 mm) of the ends of the threads 51 inserted into between the looking plate 541 and the elastic plate 542. Consequently, the ends of the threads 51 would separate from the hooking device 54 easily at the beginning of sewing, resulting in the net-like stitches falling to form at the beginning.
Another conventional sewing machine capable of making three straight stitches and a net-like stitch on each side of a cloth has upper thread cutting device 56 besides the upper shuttle 52 and the thread guide support 53; referring to FIGS. 16 and 17, the upper thread cutting device 56 cuts off the upper net thread 531, and hold the end of the same automatically at the end of a sewing. However, the ends 510 of the threads 511 for the straight stitches are not held by any clipping device when the threads 511 are cut off by the lower thread cutting device 55, so the operator of the sewing machine has to move the ends 510 rearwards with his hands such that the threads 511 are disposed between the pressing member 57 and the cloth. Otherwise, the upper net thread 531 would fail to form upper net-like stitch because the threads 511 are not disposed in a right position; when the threads 511 are disposed correctly, in the downward movement of the needles 51, the upper net thread 531, guided by the thread guide support 53, will locate between the first thread 511 (the right one) and the right one of the needles 51; thus, the upper net thread 531 can be made into net shape by the upper shuttle 52 and the thread guide support 53, and secured to the cloth by the threads 511 as shown in FIG. 18.
From the above description of the second conventional sewing machine, we can see that the sewing process is not efficient because the worker has to put the ends 510 of the threads 511 at the right position at the beginning of every sewing. Consequently, the cost is relatively high. Referring to FIG. 19, to overcome the above inconvenience, many clothes are fed to the sewing machine one after another such that the worker doesn't have to move the ends 510 of the threads 511 every time. However, the workers still have to cut off the threads between the clothes with a scissors afterwards, a waste of labor time.
From the above description, it can be understood that the conventional sewing machines have disadvantages as follows:
1. To make net-like stitches on two sides of a cloth, the sewing machine has to be equipped with the thread guide support, and the upper thread hooking device removed, i.e. the factories have to remove and install the auxiliary devices frequently for different orders placed by the customers. A small factory can't afford to hire a technician so the workers have to do the installation, resulting in problem of calibration. If the small factory sends for a technician for the installation, the cost is high, and it is a waste of time.
2. The workers have to spend much time in putting the ends 510 of the threads 511 in a right position for permitting a upper net-like stitch to be formed. And, referring to FIG. 18, relatively long end portions of the threads 511 would be left on the cloth.